In collaboration with Dr. Tseng's group at the Joslin Diabetes Center / Harvard Medical School in Boston, we generated clonal cell lines from human neck fat and characterized their adipogenic differentiation and metabolic function in vitro and in vivo after transplantation into immune deficient nude mice. Using clonal analysis and gene expression profiling, we identified unique sets of gene signatures in human preadipocytes that could predict the thermogenic potential of these cells once matured in culture into adipocytes. These data highlight the cellular heterogeneity in human BAT and WAT and provide novel gene targets to prime preadipocytes for thermogenic differentiation. In parallel, we tested the effects of diet-induced obesity (DIO) on brown adipose tissue (BAT). We fed 6-week-old C57BL/6 mice either a normal chow diet (NCD) or a high-fat diet (HFD). After 16 additional weeks, we measured body fat, WAT, and BAT mRNA expression, glucose tolerance, and rates of glucose uptake in response to insulin and the beta3-AR agonist mirabegron. We saw that compared with NCD, HFD increased body fat and impaired glucose tolerance. Both WAT and BAT had higher mRNA levels of markers of inflammation, including TNF&#945; and F4/80. Insulin signaling in BAT and WAT was reduced, with decreased Akt phosphorylation. Diet-normalized BAT glucose uptake rates were lower in response to mirabegron. These results support a model in which DIO leads to BAT inflammation and insulin resistance, leading to a broader impairment of BAT function.